New insights into the synthesis, morphology, and growth of periodic mesoporous organosilicas

Periodic mesoporous organosilicas with two-dimensional and three-dimensional hexagonal as well as cubic (Pm3n) symmetry were synthesized using bridged silsesquioxane species (RO)(3)Si - CH2 - CH2 - Si(RO)(3) as precursors and cetyl- or octadecyltrimethylammonium chloride (C(16)TMACl or C(18)TMACl) as structure-directing species. These materials were characterized by Nz adsorption, SEM, TEM, and solid-state MAS NMR spectroscopy. C-13 and Si-29 NMR data showed unambiguously that all carbon atoms were covalently linked to Si. The cubic material obtained in the presence of C(16)TMACl and 1,2-bis(trimethoxysilyl)ethane (BTME) first formed into truncated rhombic dodecahedral particles that grew into spheres. The sample prepared in the presence of C(18)TMACl and BTME at 100 degreesC was entirely comprised of concentrically self-assembled 10-mum hexagonal rods. Using C(16)TMACl in the presence of 1,2-bis(triethoxysilyl)ethane (BTEE) at 95 degreesC afforded high-quality two-dimensional hexagonal organosilica comprised of unusually long (30-40 mum) faceted empty tubules.